1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for use in the manufacturing of an SOI (silicon-on-insulator) substrate by a bonding method which involves bonding, through heat treatment or the like, two silicon substrates: a device substrate having semiconductor devices, and a supporting substrate.
2. Description of the Related Art
A bonding method, which involves bonding, through heat treatment or the like, two silicon substrates (a device substrate and a supporting substrate), is known as a method for manufacturing an SOI substrate. When manufacturing an SOI substrate by such a boding method, it is necessary to remove a peripheral non-bonded portion of bonded two substrates from the SOI substrate.
A method is known in which a first silicon substrate (device substrate), having a semiconductor layer (SIO layer) in a surface and whose peripheral portion of the surface has been polished away, and a second silicon substrate (supporting substrate), facing each other, are bonded via an insulting film, and then a back surface of the first silicon substrate (device substrate) is removed by polishing or etching, leaving the semiconductor layer (see Japanese Patent Laid-Open Publication No. H4-85827). The polishing of the peripheral portion of the surface of the silicon wafer having the semiconductor layer (SIO layer) can be carried out, e.g., with a grinding stone (see Japanese Patent Laid-Open Publication No. H4-263425).
A method is also known in which a first silicon substrate (device substrate), having a surface semiconductor layer (SIO layer), and a second silicon substrate (supporting substrate), facing each other, are bonded via an oxide film. A thickness of the first silicon substrate (device substrate) is then reduced to a predetermined thickness, leaving the semiconductor layer (SIO layer). Thereafter, a peripheral portion of the semiconductor layer (SIO layer) of the first silicon substrate (device substrate) is chamfered (see Japanese Patent Laid-Open Publication No. 2001-345435). The chamfering of the peripheral portion of the semiconductor layer is performed, e.g., by tape polishing or soft polishing.
A method for polishing a peripheral portion of a silicon substrate has been proposed. This method comprises polishing an insulating film with a polishing tape, having ceria abrasive particles fixed on it, until a silicon surface becomes exposed, and continuing polishing with a polishing tape having diamond abrasive particles which have a higher ability to polish silicon than ceria abrasive particles (see Japanese Patent Laid-Open Publication No. 2008-263027).
The applicant has proposed a polishing apparatus which can polish a peripheral portion of a substrate, including the flat portion, with a polishing tape while maintaining the original angle of the peripheral portion (see Japanese Patent Laid-Open Publication No. 2009-208214).
Removal of a deposited film (insulating film) and polishing of silicon in a peripheral portion of a silicon substrate are generally carried out by using a diamond disk. When carrying out such polishing with a diamond disk, it is necessary to accurately control the position of the polishing machine itself. The positional control of such a polishing machine is fairly cumbersome. Further, a surface of a deposited film, e.g., covering device interconnects, of a silicon substrate is likely to be stained. In addition, when a high contact pressure of a diamond disk on a silicon substrate is used in order to ensure an appropriately high polishing rate, the large pressure can cause significant damage, such as crack, to the silicon substrate. The use of a low contact pressure to prevent this problem will lead to a considerably low removal rate for a deposited film and silicon.
When a grinding stone is used to polish away a deposited film (insulating film) and silicon from a peripheral portion of a silicon substrate, it is necessary to position the grinding stone at a slight distance from, e.g., a supporting substrate so as to avoid contact with the silicon substrate. This requires high-precision positioning of the grinding stone and necessitates a special structure for that, making the apparatus construction complicated.
On the other hand, when the removal of a deposited film and polishing of silicon in a peripheral portion of a silicon substrate are carried out successively using one polishing tape, the degree of polishing of silicon can differ according to location, producing irregularities in the polished surface. In particular, in a silicon substrate having interconnects, a peripheral area where a deposited film needs to be polished away is changeable, and a thickness of the deposited film often varies according to location along the circumferential direction of the silicon substrate. Such a deposited film, in a thin portion, may be removed quickly, but it may take a considerably longer time to polish away a thick portion of the deposited film. When the polishing rate of silicon is higher than the polishing rate of the deposited film, silicon will be polished away in a considerably larger amount in those areas where the deposited film has been removed quickly. Thus, the polishing amount of silicon is likely to vary according to location in the silicon substrate.
Further, it is difficult and requires long-time polishing to control the surface roughness of a polished surface or to remove a damaged or crushed layer remaining on a polished surface. Insufficient control of the configuration or surface roughness of a polished surface will lead to difficulty in the next-step processing, such as film forming.